Many industrial and other systems employ gaseous material at a variable or intermittent rate. Examples of such systems include the use of oxygen as oxidant gas for combustion, the use of nitrogen gas for heat treating or inerting atmospheres, and the use of hydrocarbon gas as fuel. For a number of reasons including safety, convenience, and economics, it is preferred to store the gaseous material in liquid form and to vaporize the liquid to the gaseous form when needed. Thus, a typical gas supply system includes a liquid storage tank and means to vaporize the liquid to the gaseous form. A liquid pump may be used to pump the liquid to an increased pressure, and upon vaporization the high pressure gas will flow to the use point. When the gas usage is at a constant rate this is all that is needed. For this situation, the liquid pump is sized to correspond to the required constant flow rate and available constant speed constant flow units are satisfactory. However, if the gas usage is at a variable rate, a gas storage tank is needed in order to avoid gas venting during low demand time periods and to supply added gas during high demand time periods.
The constant flowrate liquid pump must be sized to match the average usage demand flow. A pump sized smaller than the average demand flow would be inadequate. A pump sized larger than the average demand flow would require either venting the gas or a large number of pump stoppages. Venting of the gas is obviously undesirable and costly. Excessive numbers of pump stoppages are also undesirable because each time the pump starts it must be recooled to the liquid temperature. This recooling expends both energy and product, and desirably is minimized for efficient operation.
Although the liquid pump must be sized to match the average usage demand flow, the gas storage tank must be sized to meet the highest usage rate for the variable rate use point. This requirement can entail high capital costs in those situations where the variable demand maximum usage rate is high compared to the average. Further, this situation can lead to high capital costs where the gas supply must be at a high pressure level, since the necessary gas storage tanks operate at even higher pressure levels. Accordingly, it is desirable to have a system which can adequately supply gas to a variable demand rate usage point at a high pressure level while allowing for the gas storage tank size requirement to be significantly reduced.
It is therefore an object of this invention to provide an improved gas supply system for variable rate gas usage at high pressure levels.
It is another object of this invention to provide an improved gas supply system for variable rate gas usage whereby the gas storage tank size requirement is significantly reduced.
It is further object of this invention to provide an improved gas supply system for variable rate gas usage wherein the need to stop and restart the liquid pump is reduced.